1. Field of the Invention
The present invention relates generally to recuperators for gas turbine engines and, more particularly, to a technique for reducing transient thermally induced stresses which result in recuperator failures referred to as "blowouts", thereby improving the operating life of the recuperator.
2. Discussion of the Prior Art
Brayton cycle engines generally utilize compressors for compressing air for the support of combustion, a combustion chamber which has inlets for both the compressed air and fuel, and means for extracting energy from the hot exhaust gases to produce mechanical work. To extract the energy, the hot exhaust gases produced in the combustion chamber are fed to a turbine that rotates a drive shaft. In a recuperated turbine engine, exhaust gases from the turbine are passed through a recuperative heat exchanger that heats the relatively cold compressed air from the compressor to maximize efficiency of the engine. The purpose of the recuperator, or regenerator as it is sometimes called when it is of a rotating construction, is to return some of the heat energy that would normally be lost with the exhaust, to the front of the combustion chamber. By doing this, less fuel is required to reach the turbine limiting temperatures and this will result in high thermal efficiency, low specific fuel consumption, and low exhaust gas temperature. Recuperators are commonly used on ground-power engines, but to a lesser extent on aircraft engines since this method of power recovery often results in excessive weight and/or air-sealing difficulties.
Typical of current recuperator designs is the construction disclosed in U.S. Pat. No. 5,004,044 to Horgan et al. In that instance, an annular heat exchange apparatus is provided for radially conducting a first fluid from a center aperture to an outer perimeter and is adapted for conducting a second fluid through the apparatus. The apparatus comprises a plurality of heat exchange modules and a plurality of second fluid conduit members. The heat exchange modules each have a rectilinear heat exchange means with a first fluid inlet side at the center aperture. The first fluid inlet sides substantially define the center aperture. The plurality of second fluid conduit members are located between adjacent modules for conducting the second fluid into the modules. In terms of construction, the heat exchanger comprises a plurality of parallel corrugated plates fixedly mounted together in a housing. The corrugations cause turbulence in the flow to improve heat exchange and they simultaneously provide rigidity to the structure.
Also known to the prior art are a variety of constructions for accommodating contractions and expansions of the components thereof. These include, for example, U.S. Pat. Nos. 2,526,135 to Holmes et al. and 2,015,819 to Seligman et al. However in neither of these instances was there any construction for accommodating heat-caused expansion and contraction of components adequate to solve the problems solved by the present invention.